For some applications, shells are formed around molds to achieve a negative of the mold. The shells are then removed from the molds to be further used for various applications. One example application in which a shell is formed around a mold and then later used is corrective dentistry or orthodontic treatment. In such an application, the mold is of a dental arch for a patient and the shell is an aligner to be used for aligning one or more teeth of the patient.
One challenge with molds used to form shells is the subsequent removal of the shells from the molds. In order to ensure that a shell will be removable from a mold without damaging or permanently deforming the shell, the shapes and types of features that are included in the mold may be limited. For example, features with significant undercuts (also referred to as negative inclination) and/or complex features may impair the removal of the shell from the mold.